There is a story from some years ago that talks about an experiment that scientists were performing.  In this experiment they were growing the "perfect" ecosystem.  They gathered and created the perfect soil for growing conditions and created the perfect balance of sunlight and humidity in the bio-dome that they created for the experiment.  And then they planted the seed and tended the gardens and set about observing what would happen.  And one of the interesting results of the experiment was that the trees would only grow to a certain height and then they would simply fall over.  The scientists puzzled over this result for a while as everything in the growing conditions was perfect.  This result seemed anomalous.  What the scientists then realized what was missing in their experiment was the wind.  The replication of the wind was excluded from the experiment because it was thought to be a variable that hampered growing; and in a certain way it is.  But the wind and the challenge and adversity it created causes trees to grow stronger with deeper roots.  It is the adversity of fighting the wind that causes trees to be strong.  And our lives are the same.  We need challenge and we need adversity to grow stronger as individuals, whether physically or mentally.  It is the presence of adversity that stretches us and causes us to grow.

Strength does not come from winning. Your struggles develop your strengths. When you go through hardships and decide not to surrender, that is strength.  Arnold Schwarzenegger

The world breaks everyone, and afterward, some are strong at the broken places.  Ernest Hemingway

Out of suffering have emerged the strongest souls; the most massive characters are seared with scars. Khalil Gibran